Can you judge someone's faithfulness by their face?


Thanks to the Ashley Madison hack, we can now, theoretically, identify cheaters simply by searching for them online. But what if we could identify cheaters simply by looking at their faces? According to recent research, we can—sort of.

In the study, published in the peer-reviewed journal PLOS One, researchers at the University of Western Australia found that, when presented with photos of two different women, men were able to select the more faithful of the two. While they didn’t always choose correctly, they performed better than what would be expected by chance.

It worked like this. Following in the footsteps of previous research that examined women’s ability to correctly judge a man’s fidelity—one study suggested they can, to a minor extent—lead evolutionary psychologist Samantha Leivers and her team asked 103 men to select which woman from a pair of photos was more faithful. Within each pair, one of the two women had admitted to cheating on a partner at least twice.

It turned out the men successfully chose the faithful woman 55 percent and 59 percent of the time in two trials. Sure enough, with a margin of error of 1.4 percent in both trials, the men performed slightly better than if they had just chosen at random.

Perhaps not surprisingly, the men also perceived the more “faithful” of the two women as more trustworthy—suggesting men may use trustworthiness as a sign of sexual fidelity.

The authors acknowledge, though, that more may be going on than meets the eye. The seeming correlation between a woman’s faithfulness and her trustworthiness may be subtly influenced by perceived emotions from her facial expressions—and men may have relied on these perceived emotions to make their judgments.

While only 17 pairs of photos were used for the study, Leivers says seeing “consensus in trait judgments”—in other words, agreement among participants regarding who looks faithful and who doesn’t—when presented with photos “is fascinating.” That said, because the men did not accurately choose the more faithful woman in all photo pairs, certain pairs may have been an easier call than others.

Why might some men have this seeming gift of being able to suss out cheats? According to Leivers, men could have evolved the ability to avoid reproducing with a partner who commits sexual infidelities. If his partner turns out to be unfaithful, a man is more likely to find himself the victim of cuckoldry—investing a great amount of parental resources to raise an offspring that is not his own.

Alternatively, in what may be good news for people interested in open relationships, a man’s ability to accurately judge a woman’s faithfulness could help him identify partners who might be willing to engage in his infidelities, says Leivers.

In either case, this ability could help ensure a man’s reproductive success, says Leivers, potentially allowing him to have more children over a lifetime and ensure he is passing down his genes.

Intriguing as they are, some dispute the findings from this rather small and limited study. As David Buss, a psychologist at the University of Texas who studies the evolutionary psychology of mate selection, told me in an email, “Whether men have evolved an adaptation specifically for detecting a woman’s likelihood of fidelity or infidelity purely from facial cues seems a bit […] dubious.”

Buss believes that other behavioral cues, including a woman’s flirtatiousness and her sexual reputation, provide more reliable information in the real world—and would have been valuable to early humans, who lived in small groups. Nevertheless, he thinks the results are “certainly interesting” if they can be replicated.

As with all small studies, much more research is needed to determine if it’s really a thing.

Correction: We originally stated that 147 men participated in the photo selection task, when it fact, only 103 took the test. The larger number participated in other aspects of the study.

Joyce Pieretti is a graduate student in evolutionary biology at the University of Chicago.

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